We will continue our studies on the "major protein complex", a group of very abundant proteins exposed on the surface of the E. coli outer membrane. These proteins cover much of the surface of the cell, are receptors for viruses and bacteriocins, and are cell surface antigens. Several of these proteins have been shown to function as pores in the outer membrane, allowing passage of small nutrient molecules, antibiotics, etc. through the outer membrane. We will examine the diversity of these proteins in various strains and species by comparison of electrophoretic profiles and peptide maps, with the objective of determining the extent of genetic polymorphism of these proteins. E. coli K-12 has several silent genes coding for surface proteins, and we will try to find out how many different silent genes are present and whether they are present or expressed in other strains. By the study of mutants missing these proteins we will study the mechanism by which these proteins are synthesized and translocated to their site on the cell surface. We will attempt to find the function for one group of proteins for which no function is known, but which is present in all gram negative bacteria. We will attempt to improve our ability to prepare antisera against these proteins, and will determine the role they play in the bactericidal action of serum complement.